High-brightness, compact illuminator with integrated optical elements

ABSTRACT

A compact, high-brightness, integrated illuminator in which collection of light from a point-arc source is maximized by a multi-curvature reflector section configuration of elliptical reflector and segmented spherical retroreflector directing all light rays into a well-defined numerical aperture. The invention also integrates a homogenizer and other optical elements with the multi-curvature reflector section, constructs any or all of these components in a single block of optical material, or, alternatively, constructs these components with molded hollow reflective cavities fabricated in metal or plastic blocks. Cooling is provided by internal fluid channels within the block.

FIELD OF THE INVENTION

This invention relates to light sources and illumination systems foroptical projection, and specifically relates to such applications inwhich it is important to maximize the light collection from a sourcelamp, to minimize the size and power requirement of the lamp, to makethe spatial uniformity of the lamp's light beam high, and to collect thelight within a specified numerical aperture so as to optimize theimaging performance of the projection system.

BACKGROUND OF THE INVENTION

A key subsystem in optical systems for a variety of applications is anillumination system which comprises a light source, such as an arc lamp,and several optical components, such as mirrors and lenses, to collect,shape and relay the light from the source to the desired destination.For example, in a projector, light from an arc lamp is collected, madeuniform, and made to illuminate an object, such as film or aprogrammable spatial light modulator, which is then imaged onto adisplay screen. As another example, in a lithography system, light fromthe light source is collected, made uniform, shaped into a specificcross-section, and is made to illuminate a photomask having a pattern.The mask is then imaged by a projection lens to a substrate, such as asemiconductor wafer or a display panel, coated with a layer ofphotosensitive medium.

In all these applications, the intensity of the light illuminating theobject must be very uniform spatially. The object, as stated earlier,is, for example, a spatial light modulator (SLM) chip in a projector, ora photomask in a lithography system. Spatial uniformity of a light beammeans that the cross-sectional profile of the intensity must besubstantially flat. A second important requirement on the illuminationsystem is that its efficiency must be as high as possible so that lossof light is minimized and the smallest possible light source may beused. Alternatively, the highest possible energy may be obtained at thedestination surface, such as the display screen or the semiconductorwafer.

Other highly desirable features in an illumination system includecompact size and self-luminosity. The importance of a compact size ofthe illumination system is self-evident—it enables the whole opticalsystem to be compact, and therefore, low-weight, more portable, etc.Self-luminosity of a light source means it is equivalent to an emissionsurface on which every point behaves effectively as an emission pointfrom which light rays emanate in a specific numerical aperture. Such acharacteristic is especially important when the illuminated object mustbe subsequently imaged with high resolution onto another surface. All ofthe above desirable features of illumination systems are important inthe case of digital projections, lithography systems, and numerous otheroptical systems.

A self-luminous emission surface is readily obtained by transformationof a high-brightness, point-like light source by use of suitable opticalelements. A widely used, high-brightness, point-like light source is ahigh-pressure, compact, Hg (or Hg—Xe) arc lamp. To increase the amountof collected radiation, and direct it toward the object, such an arclamp is usually manufactured with a built-in elliptical reflector. Anelliptical reflector has two focus points, which I shall call “nearfocus” and “far focus.” The point-arc of the lamp is situated at a focuspoint of the elliptical reflective surface, which causes the reflectedrays to be directed toward the other focus point of the ellipse,enabling them to enter a beam-uniformization device at a desirednumerical aperture. In all such light sources, the requirement ofmaximum collection efficiency on the one hand and a well-definednumerical aperture on the other hand cannot both be met optimally. Thisis so because, to maximize light collection, one must use as large aportion of the elliptical surface as possible, whereas to confine thereflected rays to the desired numerical aperture, one must limit theextended arc of the reflector.

SUMMARY OF THE INVENTION

This invention eliminates the need for a trade-off, in an illuminationsystem, between the two desired requirements—collection efficiency andwell-defined NA. This invention provides a light source configurationwith the maximum possible light collection efficiency, and directs allthe collected light into the pre-designed numerical aperture. Further,the disclosed configuration also provides integration of an uniformizerdevice into a single compact module. Finally, the reflector housing andbody are so designed that cooling channels can be built into the lampconstruction for cooling the lamp, with air or with a liquid in aclosed-loop system.

This invention discloses a construction for a compact arc lamp in whichcollection of light from a point-arc source is maximized by amulti-curvature reflector section configuration in such a way that notonly all of the collected radiation is focused at a point, but it isalso directed into a well-defined numerical aperture. The invention alsoshows how such a high-efficiency lamp is integrated with an intensityhomogenizer, making it possible to provide a compact, integrated lightsource for applications in projectors, displays, projection television,and exposure systems. As illustrated in FIG. 1, a point-arc source 1 isplaced at the near focus 2 of an elliptical reflector 3, which directsthe reflected rays (e.g., 4) to the far focus 5 of the ellipse 6. Thearc-extent (from 7 to 8) of the elliptical reflector 3 is such that theoutermost light rays (reflected from near its perimeter, e.g., 9) definethe desired numerical aperture α, for the radiation. I shall thereforecall them “intra-NA rays.” All other light rays, which I shall call“extra-NA rays,” in prior art lamp designs would be lost because theywould not be directed to the far focus 5 of the ellipse. The loss ofsuch rays could be reduced by extending the arc of the ellipticalreflector, but then the numerical aperture of the collected rays wouldincrease beyond the desired angle. In this invention, the loss of these“extra-NA rays” is eliminated by constructing the lamp reflector asfollows:

The NA-defining arc of the reflector surface is made elliptical, asstated. Beyond the solid angle subtended by this arc, the reflectingsurface is extended by a series of spherical segments 10-13 whose centeris the near focus 2 of the elliptical surface. All extra-NA light raysstriking these spherical segments (e.g., 14) are directed back towardand through the near focus 2, so that when they are then reflected bythe elliptical surface behind the near focus, they are brought to afocus at the same far focus 5 of the ellipse where all the “intra-NA”rays, which were reflected directly by the elliptical surface, arefocused. I shall call such a reflector an “EllipSpheRetro Reflector,” orESR Reflector. The lamp construction of this invention thus nearlydoubles the “useful” light efficiency of the lamp. In addition, as alsoillustrated in FIG. 1, a solid light-tunnel homogenizer 15 is integratedwith the reflector enclosure, rendering the integrated unit extremelycompact and manufacturable at a low cost. In the Detailed Description ofthe Embodiments, I describe several such reflector designs andintegration configurations.

An object of the invention is to make useful all of the light from anarc lamp by combining an elliptical reflector with a set of concentricspherical retro-reflector segments.

A feature of the invention is the positioning of the center of thespherical reflector segments, at the near focus of the ellipticalreflector, to retain the numerical aperture.

Another feature of the invention is the segmenting of the sphericalreflector to maintain the focus at the near focus of the ellipticalreflector while minimizing the outer envelope of the segmented sphericalreflector and thus the overall size of the lamp-reflector subassembly.

Still another feature is the combination of homogenizer with ellipticalreflector and spherical retro-reflector segments for compactconfiguration.

Yet another feature is the embodiment of the combination of homogenizerwith elliptical reflector and spherical retro-reflector segments as asolid block of material for good thermal management characteristics andeasy manufacturability.

An advantage of the invention is the high brightness of the lamp withhigh efficiency of light collection.

Another advantage of the invention is its integrated configuration thatcombines a lamp and reflectors with uniformizer and other opticalelements.

Yet another advantage of the invention is its compactness consistentwith good optical and heat-dissipation qualities.

Other objects, features and advantages will become clear to thoseskilled in the art during reading of the following text and perusal ofthe attached drawings.

FIGURES

FIG. 1 is a schematic illustration of the concept of the invention,showing a short-arc lamp in a reflector cavity with an ellipticalforward-reflecting surface, spherical retro-reflecting segments, andwith a joined intensity homogenizer.

FIG. 2 shows a prior-art arc-lamp with an elliptical reflector,illustrating how a majority of the forward-emitted rays from the lampare not collected.

FIG. 3 is a further illustration of a prior-art lamp, showing how anextension of the elliptical reflector does not improve collection offorward-emitted rays.

FIG. 4 is a schematic of one of the embodiments of the invention,showing a short-arc lamp with an elliptical reflector and a sphericalretro-reflector for collection of all the forward-emitted rays.

FIG. 5 is an illustration of a preferred embodiment of the invention,showing a short-arc lamp in a reflector housing, the reflector having anelliptical section and several spherical retro-reflecting segments.

FIG. 6 is an illustration of another preferred embodiment of theinvention, showing a short-arc lamp within a reflector block enclosuremade of two blocks, the reflector surface having an elliptical sectionand spherical segments.

FIGS. 7 and 8 are illustrations of the end views of the embodiment ofFIG. 6.

FIGS. 9 and 10 are illustrations of the end views of an embodiment ofthe invention similar to that of FIG. 6, except that the outer perimeterof the cross-section of the reflector block assembly is circular ratherthan square.

FIG. 11 illustrates an embodiment of the invention showing a short-arclamp in a reflector block assembly similar to that of FIG. 6 but withthe addition of built-in cooling channels.

FIG. 12 is an end-view of the embodiment of FIG. 11.

FIG. 13 is a preferred embodiment of the invention showing a short-arclamp in a block enclosure that has an elliptical reflector surface,spherical retro-reflector segments, and a light-tunnel homogenizersection.

FIG. 14 is an embodiment of the invention showing a short-arc lamp in areflector block housing that also has an imaging lens.

FIG. 15 is an illustration of a preferred embodiment of the invention,showing a short-arc lamp housed within a two-piece block assembly, theblocks fabricated to provide an elliptical reflector surface, a set ofspherical retro-reflecting segments, a light tunnel homogenizer section,and an imaging lens.

FIG. 16 illustrates the construction details of the embodiment of FIG.15, showing how the entire assembly is made of two molded sections.

FIGS. 17 and 18 present three-dimensional perspectives of theillustrations of FIGS. 15 and 16.

FIG. 19 is an illustration of a preferred embodiment of the invention,showing a short-arc lamp housed within a two-piece block assembly, theblocks fabricated to provide an elliptical reflector surface, a set ofspherical retro-reflecting segments, a fly's-eye-lens homogenizercombined with a collimating lens, and an imaging lens.

FIG. 20 illustrates the construction details of the embodiment of FIG.17, showing how the entire assembly is made of two molded sections.

FIG. 21 is an illustration of a preferred embodiment of the invention,showing a short-arc lamp housed within a two-piece block assembly, theblocks fabricated to provide an elliptical reflector surface, aspherical retro-reflecting segments, an energy-recycling light tunnelhomogenizer section, and an imaging lens.

FIG. 22 is a preferred embodiment of the invention showing a short-arclamp in a block enclosure that has an elliptical reflector surface,spherical retro-reflector segments, and an energy-recycling solidlight-tunnel homogenizer section.

DETAILED DESCRIPTION OF THE EMBODIMENTS

Arc lamps are used as light sources in a wide variety of applications,such as electronic data projectors, film projectors, projectiontelevisions, and exposure systems for microelectronics fabrication. Atypical prior-art construction of an arc lamp is shown in FIG. 2. Itcomprises a short-arc, high-pressure, Hg or Hg—Xe discharge lamp 20,with an elliptical reflector 21, and is sealed with a window 22 in thefront. The point-arc of the lamp is placed at the near-focus 23 of thereflector's elliptical surface. Light rays incident on the reflectorsurface are directed toward the far focus 24 of the ellipse, from wherethey may be directed toward an object surface in various prior-art ways,such as with a positive lens 25. Note that among all the rays emitted bythe lamp, the effectively useful rays are only those that first reachthe point 24 and are then directed by lens 25, i.e., only the raysemitted by the arc that first strike the elliptical reflector.Therefore, all the rays, such as 26-31, emitted in a forward conedefined by the angle β, are not collected, and are thus lost. Note thatthese lost rays cannot be collected by simply extending the ellipticalarc-extent of the reflector—as shown in FIG. 3. If the ellipticalreflector arc is extended by the portion 32 so as to prevent ray 30 fromescaping, then ray 30 will be intercepted, and, after reflection as ray33, will reach the far focus 24. Even so, rays such as ray 33 still willnot be collected by lens 25 because they are extra-NA light rays,outside the collectible NA, and therefore will be lost. Depending uponthe lamp dimensions, these lost rays may constitute a third or half ofthe total radiation emitted by the lamp. Thus, if these otherwise lostrays could be effectively collected, the useful light efficiency of thelamp could be increased by as much as a factor of 2. Such is theimprovement made possible by the invention described in thisapplication.

Effective Collection of “Extra-NA” Light Rays

At the outset, let me clarify the distinction between “effectivecollection” and mere collection of light rays. Referring to FIG. 3, thelight ray 30, upon reflection from the elliptical reflector segment 32,is collected as ray 33 and directed to the focus point 24, but suchcollection is not useful because ray 33 is not accepted by lens 25. Whena ray emitted by the lamp arc is so directed that it is within theacceptance cone of the lens 25, i.e., it is an intra-NA ray, within thespecified numerical aperture, I shall term its collection as “effectivecollection.”

Now I describe how the extra-NA rays can be effectively collected,thereby increasing the effective brightness and efficiency of the lampsubstantially.

FIG. 4 illustrates the basic principle of the new EllipSpheRetro (ESR)lamp concept. The lamp envelope is designed to include not only theelliptical reflector 21, which collects, as before, all the intra-NArays, but also a spherical reflector 35 whose arc-extent is such that itcaptures all the extra-NA rays such as rays 36-43. Further, thecurvature and placement of the spherical reflector 35 are such that itscenter is the same as the near focus 23 of the elliptical reflect 21.Therefore, an extra-NA ray, such as ray 37, is retro-reflected by thespherical reflector 21, travels through the near focus 23, is reflectedby the elliptical reflector 21, is directed as ray 44 through the samefar focus 24, and is angularly confined within the specified NA. Thus,by capturing nearly all the extra-NA rays which otherwise would be lost,this ESR reflector lamp nearly doubles the radiation delivered to theimaging lens 25 within the desired numerical aperture. Note that thewindow 22 which previously (see FIG. 3) functioned as the front face ofthe lamp enclosure, is now not necessary; it is therefore eliminatedand, instead, a window 45 is provided as a seal on an opening in thespherical reflector 35. I will describe other embodiments of the lampconstruction shortly.

Compact ESR Reflector Lamp Configuration

Note that in the embodiment of the invention illustrated in FIG. 4, theincorporation of the spherical retro-reflector nearly doubles the sizeof the overall enclosure of the lamp, which is not a desirableconsequence. Such an increase in the lamp size is prevented by theembodiment shown in FIG. 5. Here, the previous spherical reflector 35 isbroken up into several spherical segments 46-51. Each of the sphericalsegments 46-51 has a curvature and position such that its center is atthe same near focus 23 of elliptical reflector 21. Additionally, thepartitioning of the previous spherical reflector 35 into the newspherical segments 46-51 is done in such a way that it becomes possibleto place the new segments as close as possible to the outermost rays 52and 53. These outermost rays 52 and 53 define the specified numericalaperture a. Note that, constructionally, each pair of equivalentspherical segments, e.g., 46 and 51, are together a strip-slice of aspherical shell. Additionally, note that the largest-radius segments 48and 49 are constructionally a spherical disc, and that this disc has ahole in the center where the far focus of the elliptical reflector 21 issituated; this hole is sealed with the optical window 45, as shown inFIG. 5.

Block Configuration with Reflector Cavity

The ESR Reflector lamp design illustrated in FIG. 5 may be readilyconstructed in practice as a block enclosure in which the reflectorsurface is realized by forming a cavity. This is illustrated in FIGS. 6,7 and 8. The full enclosure is made as two halves 55 and 56, each ofwhich has one-half of the lamp cavity hollowed out from inside andcoated with a durable, high-reflectivity coating. The ellipticalreflector surface is indicated by 60 and the spherical reflectorsegments by 61-63.

FIG. 7 is an end-view of the lamp, looking at FIG. 6 from the left, andFIG. 8 is the end-view of the lamp looking from the right. The perimeterof the cross-section of the enclosure is shown as a square (FIGS. 7 and8). As an alternate embodiment, the perimeter can be circular, asillustrated in FIGS. 9 and 10. The two half-blocks of the enclosure canbe joined with each other using a suitable high-temperature adhesivealong the interface 57. Provision is made on the left end-faces (FIGS. 7and 9) for an end of the arc lamp discharge tube 58 and electrodes 59 toemerge. On the right end-faces, the transparent window 45 is suitablysealed.

High-Brightness-Lamp Enclosure with Cooling

Since the high-brightness lamp configurations shown in FIGS. 6-10dissipate 100-200 W of power, it is highly desirable to provide abuilt-in cooling mechanism in their enclosures. The constructionsillustrated in FIGS. 6-10 enable very convenient incorporation ofcooling channels, as shown in FIGS. 11 and 12. The cooling channels maybe formed at the time the half-blocks are molded, and run through thesolid walls of the reflector half-blocks. The cooling fluid may be air,water, ethylene glycol solution or some other suitable coolant. Thechannels may continue from one half-block to the other half-block, inwhich case appropriate fluid-tight seal is provided between the twohalf-blocks. Note that the path of the cooling channels, as well astheir construction shown in FIGS. 11 and 12, is only one of may possiblepaths of embedding the channels in the reflector housing; variousalternate but equivalent configurations can readily be devised by oneeven cursorily knowledgeable in the art.

In some optical devices, when rays emitted from a point source aredirected back to the source, some instability of the source or excessiveheating may occur. In an arc lamp of the type envisioned here, thetypical size of the emission region is 1-2 mm, for which suchundesirable effects are not expected to occur. However, to eliminatesuch a possibility entirely, the spherical retro-reflector segments canbe readily designed to be slightly off their perfect position orcurvature so that the retro-reflected rays are focused suitably offsetfrom, but close to, the near-focus of the elliptical reflector.

ESR Lamp with Homogenizer

The compact high-brightness lamp with the ESR reflector described abovecan be further enhanced in functionality by integration of an intensityhomogenizing component, as illustrated in FIG. 13. The reflector unit isconfigured as before, i.e., as a combination of an elliptical reflector60 and segmented spherical retro-reflectors 61-64, integrated as a blockassembly 65, as in FIG. 6. But now, in addition, the block assembly 65also includes a cylindrical cavity 66, whose internal surface ismirrorized, and which acts as an intensity uniformizer. The cylindricalcavity 66 functions as a light tunnel with internally reflective walls.All the light rays emitted from the arc lamp and collected by theelliptical and spherical reflectors are focused near the entrance to thelight tunnel homogenizer 66. These light rays enter light tunnelhomogenizer 66 as shown in FIG. 13. The light rays get randomly mixed,by multiple reflections within the homogenizer, so that the spatialintensity distribution at the exit plane 68 of the homogenizer is highlyuniform.

Note that the homogenizer tunnel is sealed by a transparent window 45 atthe exit plane. The exit plane 68 of the homogenizer may now beconveniently imaged by a lens 25 onto the desired object surface.Suitable cooling channels may be provided in the reflector blockassembly as described previously, with FIGS. 11-12.

ESR Reflector Lamp with Integrated Lens

In the embodiment of FIG. 6, I have shown a lamp enclosure made of tworeflector blocks 55 and 56 and a transparent window 45. In addition, anexternal lens 25 is used to direct the collected rays to the objectsurface. I now illustrate how the entire assembly can be furthersimplified and made easier to fabricate at a lower cost by integratingthe lens as a part of the reflector blocks and eliminating the window,as shown in FIG. 14. The lamp enclosure is made of two reflector blocks70 and 71, and the lens 72 is made a part of one of them (70). Note thatthe lens 72, as a part of block 70, is brought into contact with block71 at interface 73; keeping the body of the lens free of additionalinterfaces enables it to have high optical performance.

Note that only the elliptical (74) and spherical (e.g., 75)retro-reflector portions of the internal surface of each block aremirrorized. In addition, the surfaces of the lens 72 may be coated withan anti-reflection coating to minimize unwanted reflection losses. Also,as in the embodiments of FIGS. 11 and 12, cooling channels may befabricated in the blocks 70 and 71.

Elliptical-Spherical Lamp with Integrated Homogenizer and Lens

The embodiments described in FIGS. 13 and 14 may be combined to providea new embodiment in which the lamp enclosure is integrated with both ahomogenizer and a lens; this is illustrated in FIGS. 15-18. The entireassembly is constructed of two blocks 70 and 71. Each block has one-halfof the elliptical reflector 74, the spherical retro-reflector segments(e.g., 75) and the homogenizer tunnel 66. The lens 72 is made entirely apart of block 70, as shown in FIG. 16, and makes contact with block 71at interface 73. Again, cooling channels may be provided in the body ofeach block. The surfaces of the reflectors and homogenizer aremirrorized. The lens surfaces are anti-reflection coated.

In all of the embodiments above in which a light-tunnel homogenizer isincorporated (e.g., FIGS. 13 and 15) it is also possible to provide adifferent type of light homogenizer as an alternative to thelight-tunnel type 66. For example, in FIGS. 19 and 20, I illustrate howa fly's-eye lens type of uniformizer 76 may be fabricated as a part ofone of the two blocks 70 and 71 that make up the lamp enclosureassembly. As before, I show the elliptical reflector as 74, one of thespherical retro-reflector segments as 75 and the imaging lens as 72. Thefly's-eye lens array 76 is a two-dimensional array of small lenslets andis readily fabricated by well-established molding processes. The lensarray 76 comes in contact with block 71 at interface 77. Note that Ihave also shown the input surface (left side) 78 of the fly's-eye lensarray 76 as a convex surface; this serves to collimate the rays insidethe body of the fly's-eye lens array. Many other alternateconfigurations are possible, such as fabricating a collimating lensseparately or using two fly's-eye lens arrays.

Compact, High-Efficiency Lamp with Integrated Energy-RecyclingHomogenizer

The efficiency and brightness of the compact ESR illuminator shown inFIG. 15 can be further enhanced by providing an energy-recycling featurein the homogenizer 66. This is especially important in the use of suchan illuminator in, for example, an electronic data projector or aprojection television where the lamp power, compactness and brightnessare significant criteria in product design. In a color projector, thewhite light from the illuminator first passes through a color filterunit, which is usually a color wheel with red, green and blue spiralbands. Each band transmits only one color. For example, light of onlyred frequency passes through the red band, the rest (approximatelytwo-thirds of the total) being reflected and lost. By using a recyclinghomogenizer, the reflected rays are captured and re-utilized, asillustrated in FIG. 21.

In FIG. 21 a ray 80 leaves the elliptical reflector 74, enters thehomogenizer 66, is reflected from the bottom homogenizer wall 83,emerges from imaging lens 72 as ray 81, and strikes color filter unit79. The frequencies of light that do not pass through filter 79 arereflected as ray 82, which, traveling in the reverse direction, passesthrough the imaging lens 72, re-enters the homogenizer 66, is reflectedfrom the bottom homogenizer wall 83 as ray 84, and strikes the innerside 85 of the homogenizer input face. The inner face 85 is mirrorized,so the ray 84 is reflected as ray 86, which is now traveling in theforward direction, and emerges from imaging lens 72 as ray 87, thusbeing re-utilized. The energy-recycling feature of this embodiment canincrease the efficiency and brightness of the illuminator by a factor oftwo or more. To maximize the energy recycling multiplier, the area ofthe homogenizer inner face 85 must be made as large as possible, andtherefore, the entrance hole 88 as small as possible. Note that theminimum size of entrance hole 88 will be determined by the focus spotsize of the elliptical reflector 74, and therefore also on the size ofthe point arc 2 of the lamp 1. I remark that the entire illuminatorassembly can be constructed, as before, of two blocks 70 and 71, inwhich cooling channels may also be provided if desired.

Illuminator with Solid Homogenizer

In the embodiments shown in FIGS. 13, 15 and 21, 1 have described alight-tunnel homogenizer that is hollow and in which the multiplereflections of the rays take place from mirrorized walls. Alternatively,the light-tunnel homogenizer can be made as a solid rod of a highlytransparent optical material such as fused silica or a suitable glass.In such a solid homogenizer, the reflections of the light rays takeplace by the phenomenon of “total internal reflection” (TIR). Such anembodiment is shown in FIG. 1 in which 15 represents the solid rodhomogenizer. The cross-section of the rod may be circular, square,rectangular or hexagonal. Since the angle of incidence in total internalreflection must be greater than the “critical angle” (given bysin−1(1/n) where n is the refractive index of the rod material) themaximum numerical aperture (NA) of the light cone is limited. If it isdesired to have an NA greater than such limit, the surface of the rodmay be mirrorized. I wish to point out that the exit face (16 in FIG. 1)of the homogenizer should preferably be coated with an anti-reflectioncoating to eliminate the nearly 4% reflection loss that would otherwisetake place at an uncoated glass-air interface.

An embodiment of the compact, high-brightness illuminator of thisinvention with a solid homogenizer having the energy-recycling featureis sown in FIG. 22. Note that in order to provide a reflective innersurface 90 for the input face of the solid homogenizer 15, thehomogenizer input face must be separated from the end face 91 of thereflector block 92 by a slot 93, and surfaces of the slot must bemirrorized. Note that the portion of the homogenizer input face wherethe forward-traveling light rays enter must be left unreflective (orpreferably even made anti-reflective). Therefore, the reflective portionof the inner surface of the homogenizer input face is a smaller fractionof total input face area in a solid homogenizer than in a hollowhomogenizer because the focus region 87 in FIG. 22 can be right at theinput face of the hollow homogenizer 66, whereas the focus region 94 inFIG. 22 must be at some distance from the input surface of the solidhomogenizer 15 so as to avoid damage to the input surface. Thus, ingeneral, it may be expected that the energy-recycling efficiency of ahollow homogenizer may be greater than that of a solid homogenizer.However, the greater reflectivity from the walls in case of totalinternal reflection may favor the hollow homogenizer. The choice betweenthe two will depend on the specific design criteria for a particularapplication.

In the description of the invention and its selected embodimentspresented in this application, I have necessarily concentrated on anelliptical forward reflector, spherical segments as retro-reflectors,and light-tunnel and fly's-eye types of homogenizers. Clearly, to thoseskilled in the art, other variations will be imaginable to achieve thedesired functionality of the invention. The broad theme of the inventionis that it provides a compact, high-efficiency arc-lamp illuminator withthe following fundamental design characteristics:

It collects most of the rays emitted by the arc in the backwarddirection by a forward-reflecting curved reflector and directs them intoa specified cone angle or numerical aperture;

-   -   it collects most of the rays emitted by the arc in the forward        direction, that otherwise would be lost, by curved        retro-reflector segments and directs them into the same        numerical aperture;    -   it uniformizes the transverse intensity distribution of the        radiation so collected by mixing the rays using a homogenizer;    -   it images the uniformized radiation of the specified numerical        aperture onto an object;    -   it simplifies the construction of the illuminator assembly by        integrating the above functions into a uniform number of        components; and    -   it provides built-in cooling capability to remove the        lamp-generated heat.

The end result of the above features is an arc-lamp illuminator thatmaximizes brightness and efficiency and minimizes size and power.Variations on the described embodiments that achieve the above featureswill be considered within the scope and spirit of this invention.

Materials

The invention lends itself to low-cost, high-volume manufacturing aswell as easy prototyping and pilot production prior to volumemanufacturing. A prototype may be easily machined from a metal such asaluminum or steel, or cast from a low-melting-temperature metal or metalalloy with or without further treatment by machining. Short productionruns may even be made using such metal prototypes, with mirrorizedsurfaces as necessary. Such metal prototypes may then conveniently beused as models for production molds to be made of glass or other opticalmaterials. In some cases, suitable plastic may be used in prototypes oreven in production, with appropriate mirrorizing, cooling and explosionprotection as necessary. For final production in quantity, glass orother optical materials are typically chosen, but since plastics andmetals are easier to machine and weld or cement, the materials choice isvery wide. This choice of materials for volume manufacturing as well asfor prototyping and short production runs provides great economy of bothproduction and design.

Utility

In addition to their use in electronic data projectors, displays andprojection television, these Illumination devices have widespreadutility wherever high-intensity forward light beams are desired. Thisincludes landing lights for aircraft and headlights for automobiles, aswell as a great variety of projection uses such as projection intheaters and arenas.

The invention has been shown in a number of embodiments and a number ofalternative configurations. Changes in these, and other embodiments andalternative configurations will be apparent to those skilled in the art,without departure from the spirit and scope of the invention as depictedin the following claims:

1. A compact, high-efficiency illumination system, characterized by: alight source; a forward-reflecting curved reflector (FRCR) to collectbackward-emitted rays from said light source, so designed that raysreflected from it are substantially directed into a desired cone angle,the numerical aperture (NA); a backward-reflecting curvedretro-reflector (BRCR) to collect substantially all forward-emitted raysfrom said light source, to reflect them toward said FRCR, forre-reflection directed into said desired cone angle; and exit port meansin said backward-reflecting curved reflector to permit light within saiddesired cone angle to exit the illuminator for use.
 2. A compact,high-efficiency illumination system according to claim 1, furthercharacterized by: a beam uniformizer to accept light rays of said NA andmix them in such a way as to produce a uniform spatial intensityprofile.
 3. A compact, high-efficiency illumination system according toclaim 2, further characterized by: an imaging lens to relay said uniformspatial intensity profile onto an object plane.
 4. A compact,high-efficiency illumination system according to claim 1, furthercharacterized in that: said light source is substantially a pointsource; said forward-reflecting curved reflector is substantiallyelliptical in shape, having a near-focus and a far-focus; said lightsource is located substantially at the near-focus of said ellipticalcurve of said forward-reflecting curved reflector so that the light raysforward-reflected from said forward-reflecting curved reflector aresubstantially directed at and through the far-focus of said ellipticalcurve of said forward-reflecting curved reflector; and said exit portmeans is situated in the vicinity of said far-focus to permit exit ofsaid light rays directed into said desired numerical aperture.
 5. Acompact, high-efficiency illumination system according to claim 4,further characterized in that: said light source is a short-arc lamp inwhich a point light source emits light rays in multiple directions.
 6. Acompact, high-efficiency illumination system according to claim 5,further characterized in that: said light source is a compact,high-pressure, short-arc lamp.
 7. A compact, high-efficiencyillumination system according to claim 4, further characterized in that:said backward-reflecting curved retro-reflector is in the shape of atleast one spherical segment whose center is at the near-focus of saidelliptical forward-reflecting curved reflector so that the raysretro-reflected from the backward-reflecting curved reflector aredirected toward the near-focus of said elliptical forward-reflectingcurved reflector.
 8. A compact, high-efficiency illumination systemaccording to claim 4, further characterized in that: the arc length ofsaid elliptical reflector is limited to produce a cone angle offorward-reflected rays equal to said defined NA.
 9. A compact,high-efficiency illumination system according to claim 7, furthercharacterized in that the cumulative arc lengths of said sphericalretro-reflector segments are such that they capture substantially allrays emitted by said lamp except those rays incident on said ellipticalreflector and those rays directed through said exit port.
 10. A compact,high-efficiency illumination system according to claim 9, furthercharacterized in that at least one further optical element is positionedin the vicinity of said exit port for further processing the cone oflight rays which exits from said exit port.
 11. A compact,high-efficiency illumination system according to claim 10, furthercharacterized in that said further optical element is a window sealing achamber enclosing said forward-reflecting curved reflector and saidbackward-reflecting curved retro-reflector.
 12. A compact,high-efficiency illumination system according to claim 10, furthercharacterized in that said further optical elements are a window and auniformizer.
 13. A compact, high-efficiency illumination systemaccording to claim 10, further characterized in that said furtheroptical elements are a window, a uniformizer, and an imaging lens.
 14. Acompact, high-efficiency illumination system according to claim 12,further characterized in that said uniformizer is a fly's-eye lensarray.
 15. A compact, high-efficiency illumination system according toclaim 12, further characterized in that said uniformizer is alight-tunnel homogenizer.
 16. A compact, high-efficiency illuminationsystem according to claim 15, further characterized in that saiduniformizer is a recycling light-tunnel homogenizer.
 17. A compact,high-efficiency illuminator, for emitting a forward-directed light beamtoward an object plane, characterized by: a light source of great pointintensity, emitting light rays in multiple directions includingforward-direction and reverse-direction; a forward reflector mountedwith respect to said light source for reflecting a substantial portionof the reverse-direction light rays in a converging beam to join atleast a small portion of said forward-direction light rays in apartially-conjoined forward-direction light beam with a selected coneangle appropriate for use at said object plane; a retro-reflectormounted with respect to said forward reflector for reflectingsubstantially all of the remainder of such forward-direction light rays,other than said small portion, back to said forward reflector forredirecting into a fully-conjoined forward-direction light beam with thesame selected cone angle appropriate for use at said object plane; andan exit port positioned in said retro-reflector for passing saidfully-conjoined forward-direction light beam toward said object plane.18. A compact, high-efficiency illuminator, for emitting aforward-directed light beam toward an object plane, according to claim17 further characterized in that: said forward reflector and saidretro-reflector are joined together as a single block with an internalchamber which is reflective; and integral further optical processingmeans mounted to accept said fully-conjoined light beam for processingafter passing through said exit port.
 19. A compact, high-efficiencyilluminator, for emitting a forward-directed converging light beamtoward an object plane, according to claim 18 further characterized inthat: said internal chamber is made reflective by a reflective coating.20. A compact, high-efficiency illuminator, for emitting aforward-directed converging light beam toward an object plane, accordingto claim 18 further characterized in that: said internal chamber iscoated to be selectively reflective to desired portions of thewavelength spectrum and to dissipate undesired portions of thewavelength spectrum by further processing including absorption into saidsingle block.
 21. A compact, high-efficiency illuminator, for emitting aforward-directed light beam toward an object plane, according to claim18 further characterized by: means integral to said single block formingfurther optical processing means, mounted for processing saidfully-conjoined light beam after passing through said exit port.
 22. Acompact, high-efficiency illuminator, for emitting a forward-directedlight beam toward an object plane, according to claim 21; furthercharacterized in that: said means integral to said single block formingfurther optical processing means also serves as an explosion-reliefelement.
 23. A compact, high-efficiency illuminator, for emitting aforward-directed light beam toward an object plane, according to claim21; further characterized in that: said means integral to said singleblock forming further optical processing means is coated for lowreflectivity for the desired portion of the wavelength spectrum.
 24. Acompact, high-efficiency illuminator, for emitting a forward-directedlight beam toward an object plane, according to claim 22; furthercharacterized in that: said means integral to said single block formingfurther optical processing means is coated for high reflectivity for theundesired portion of the wavelength spectrum and transmission of thedesired portion of the wavelength spectrum.
 25. A compact,high-efficiency illuminator, for emitting a forward-directed light beamtoward an object plane, according to claim 21; further characterized by:cooling means integral with said single block.
 26. A compact,high-efficiency illuminator, for emitting a forward-directed light beamtoward an object plane, according to claim 25; further characterized inthat: said cooling means is selected among: liquid cooling by channelswithin said single block; and air cooling by fins on said single block.27. A compact, high-efficiency illuminator, for emitting aforward-directed light beam toward an object plane, according to claim22; further characterized in that: said single block is made ofheat-transmissive material.
 28. A compact illuminator configuration:characterized by: a forward reflector section, configured as athree-dimensional elliptical segment, having a near-focus position and afar-focus position; a light source position, inside said ellipticalreflector section, effectively at the near-focus position of saidelliptical reflector section; means for mounting a point light sourcemechanism at said light source position; a spherical reflector section,configured as a set of at least one three-dimensional spherical segmentcentered about said near-focus position of said elliptical reflector,with the spherical surface of a central spherical segment essentiallycrossing the far-focus of said elliptical section with an exit gap atsaid far-focus, said elliptical and spherical reflector sections servingas an elliptical-spherical retroreflection set cooperating to directvirtually all light rays emitted by said light source at said ellipticalreflector near-focus into said exit gap with a well-defined numericalaperture appropriate for further processing at an object plane.
 29. Acompact projection light source configuration, according to claim 28,further characterized in that: said elliptical reflector section andsaid spherical reflector section are configured as a single block ofmaterial.
 30. A compact projection light source configuration, accordingto claim 29, further characterized in that: said elliptical reflectorsection and said spherical reflector section are formed by a singlereflective internal cavity and in said spherical reflector section isformed by a number of spherical arc subsections, each spherical arcsubsection being centered at the near-focus of said elliptical reflectorsection.
 31. A compact projection light source configuration, accordingto claim 30, further characterized in that: said elliptical reflectorsection and said spherical reflector section have a single reflectiveinternal cavity and said spherical reflector section is formed by anumber of spherical arc subsections, each spherical arc subsection beingcentered at the near-focus of said elliptical reflector section, and thecentral spherical arc subsection having an exit window at the far-focusof said elliptical reflector section.
 32. A compact projection lightsource configuration, according to claim 31, further characterized inthat: a condenser lens is mounted to receive a fully-conjoined lightbeam of direct rays from said light source and light rays reflected fromsaid elliptical reflector as well as light rays retroreflected from saidspherical reflector and said elliptical reflector so as to exit saidcavity at said exit window with a defined numerical aperture; and saidelliptical reflector section and said spherical reflector section areformed as a block assembly creating a single internal cavity and saidspherical reflector section is formed by a number of spherical arcsubsections, each spherical arc subsection being centered at thenear-focus of said elliptical reflector section, and said condenser lensis matched in size and position to the numerical aperture of the beamexiting from said exit port for substantially complete capture of lightrays from said light source for projection.
 33. A compact projectionlight source configuration, according to claim 32, further characterizedin that: said single block assembly also is configured with at least oneauxiliary optical element.
 34. A compact projection light sourceconfiguration, according to claim 32, further characterized in that:said single block also is configured with optical elements including ahomogenizer.
 35. A compact projection light source configuration,according to claim 32, further characterized in that: said single blockassembly also is configured with optical elements including an imaginglens.
 36. A compact projection light source configuration, according toclaim 32, further characterized in that: said single block assembly alsois configured with optical elements including both homogenizer andimaging lens.
 37. A compact projection light source configuration,according to claim 32, further characterized in that: said single blockassembly is configured as two halves which are closed and sealed inmanufacture enclosing the light source positioned on the cavity axisnear one end opposite the exit port; and at least one of said blockhalves also having at least one integrally fabricated additional opticalelement from the group of optical elements including homogenizer andimaging lens.
 38. A compact projection light source configuration,according to claim 32, further characterized in that: at least one ofsaid block halves also is configured with focus adjustment means for useduring manufacture.
 39. A compact projection light source configuration,according to claim 37, further characterized in that: said single blockassembly also is configured of two halves with integrally-fabricatedoptical elements including at least two lens elements.
 40. A compactprojection light source configuration, according to claim 37, furthercharacterized in that: said single block assembly also is configured oftwo halves with optical elements including at least one lens elementadjustably attached to one of said block halves so as to be positionablefor focus adjustment during manufacture.
 41. A compact, high-efficiencydirectional illuminator system comprising: a) an elliptical/sphericalreflector chamber portion having an axis with a near-focus position anda far-focus position with respect to an elliptical forward reflectorsurface, and opposing a spherical retro-reflector surface surrounding anexit port, said spherical retro-reflector surface being opposite to saidelliptical forward reflector surface; b) a point-source light emittingelement, mounted at said near-focus on said axis intermediate saidelliptical reflector and said exit port at said far-focus, arranged toemit light rays directed as follows: b1) a significant percentage ofrays directed at said elliptical forward reflector for single-reflectionout said exit port; b2) a small percentage of rays directed out saidexit port without reflection; and b3) the remaining significantpercentage of rays directed at said spherical retro-reflector surfacefor retro-reflection back to said elliptical forward reflector forre-reflection out said exit port.
 42. A compact, high-efficiencydirectional illuminator system comprising: a) anelliptical/segmented-spherical reflector chamber portion having an axiswith a near-focus position and a far-focus position with respect to aforward elliptical reflector surface, and opposing a composite segmentedspherical retro-reflector surface surrounding an exit port, saidspherical retro-reflector surface being opposite to said ellipticalforward reflector surface; b) a point-source light emitting element,mounted at said near-focus on said axis intermediate said forwardelliptical reflector and said exit port, arranged to emit light raysdirected as follows: b1) a significant percentage of rays directed atsaid forward elliptical reflector for single-reflection out said exitport; b2) a small percentage of rays directed out said exit port withoutreflection; and b3) the remaining significant percentage of raysdirected toward said composite segmented spherical retro-reflectorsurface for retro-reflection back to said elliptical forward reflectorand re-reflection out said exit port.
 43. A compact, high-efficiency,directional illuminator system according to claim 42, furthercomprising: hollow homogenizing means (66), positioned along said axis,outside said exit port while inside the same block (65) comprising saidlamp chamber.
 44. A compact, high-efficiency, directional illuminatorsystem, according to claim 42 further comprising: transmissive sealingmeans (45) located at said exit port.
 45. The method of making acompact, high-efficiency, directional illuminator system, comprising thefollowing steps: molding a solid block of material, about a sacrificialmandrel, which is to form an internal light processing cavity having areflector portion, an opposing retro-reflector portion, and an exit portaligned along an axis; splitting the block into two half-block portionsalong the axis of said internal light processing cavity; removing themandrel from said portions of said block; treating the internal surfacesof such light processing cavity for high reflection of the desiredwavelength spectrum; positioning a high-intensity point-light sourcealong the axis of said internal light processing cavity; and closing andsealing the cavity at such exit port in a manner allowing light to exit.46. The method of making a compact, high-efficiency, directionalilluminator system, comprising the following steps: molding a set ofcomplementary segments of a material, to form an enclosure for aninternal light processing cavity, having an axis and an exit port;treating the internal surfaces of such complementary segments of suchinternal light processing cavity for high reflection of a desiredwavelength spectrum; positioning a high-intensity point-light sourcealong the axis of said internal light processing cavity; and closing andsealing the set of complementary segments to fabricate a complete,internally-reflective cavity with light means in a manner allowing lightto exit at said exit port.
 47. The method of making a compact,high-efficiency, directional illuminator system, according to claim 46,in which at least one of said segments has at least one integrallyfabricated optical element: further characterized by: closing andsealing the set of complementary segments in the vicinity of such exitport by means of such integrally fabricated optical element.
 48. Themethod of making a compact, high-efficiency, directional illuminatorsystem according to claim 46 further characterized by: molding aplurality of solid segments of a material complementary in shape to forma composite block enclosing an internal light processing cavity about anaxis; treating the internal surfaces of such light processing cavity insaid solid blocks for high reflection of the desired wavelengthspectrum; mounting a high-intensity point-light source along the axis ofsaid internal light processing cavity; and closing and sealing thecavity at an exit port.
 49. The method of making a compact,high-efficiency, directional illuminator system, according to claim 48further characterized in that: at least one of said solid segments hasat least one additional optical processing element integrally fabricatedso as to be positionable across such exit port to carry out opticalprocessing of a light beam along said axis.
 50. A compact,high-efficiency directional illuminator system comprising: a) anelliptical/segmented-spherical reflector chamber portion having an axiswith a near-focus position and a far-focus position with respect to aforward elliptical reflector surface, and opposing a composite segmentedspherical retro-reflector surface surrounding an exit port, saidspherical retro-reflector surface being opposite to said ellipticalforward reflector surface; b) a point-source light emitting element,mounted at said near-focus on said axis intermediate said forwardelliptical reflector and said exit port, arranged to emit light raysdirected as follows: b1) a significant percentage of rays directed atsaid forward elliptical reflector for single-reflection out said exitport; b2) a small percentage of rays directed out said exit port withoutreflection; and b3) the remaining significant percentage of raysdirected toward said composite segmented spherical retro-reflectorsurface for retro-reflection back to said elliptical forward reflectorand re-reflection out said exit port; and an elongation of said chamber(70) to extend beyond said exit port to permit post-focus divergence ofthe output light beam while still within the chamber; and lens means(72), integral with said single block, closing and sealing the chamber.51. A compact, high-efficiency, directional lamp system, according toclaim 50 further characterized in that: said elongation of said chamber(70) is configured as a homogenizer (66).
 52. A compact,high-efficiency, directional lamp system, according to claim 50 furthercharacterized in that: said elongation of said chamber (70) isconfigured as a fly's eye lens array.
 53. A compact, high-efficiency,directional lamp system, according to claim 50 further characterized inthat: said elongation of said chamber (70) is configured to also have acollimating lens (78).
 54. A compact, high-efficiency, directional lampsystem, according to claim further characterized in that: saidelongation of said chamber (70) opens into an air gap (93) followed by arecycling solid homogenizer (15).